The researchers sailing aboard Weatherbird II aren't studying global warming -- they're trying to end it. The ship's three-year mission, funded by for-profit eco­renewal firm Planktos, is to seed oceans with iron-rich dust, which should trigger plankton blooms. More plankton means more carbon dioxide can be pulled out of the atmosphere and trapped in the seas. The project is the first large-scale effort in a controversial field, known as geoengineering, that aims to actively combat global warming. Despite the risk of unintended environmental side effects, the Weatherbird II is already spreading iron in its wake. And it is only one of several extreme geoengineering attack plans on the table.

Restoration of Ocean Plankton

THE GOAL: Reverse plankton die-offs and reduce atmospheric CO2 levels by seeding oceans with iron, a key nutrient for plankton.

THE PLAN: Up to 600 tons of granulated iron ore will be spread in the Pacific, Atlantic and Antarctic oceans, where plankton levels have fallen steeply. Planktos says the iron won't act as a pollutant, since it will be consumed. Shoreline plankton blooms can cause oxygen depletion, but Planktos says it's not a problem in deep seas.

TIMETABLE: The Weatherbird II set sail in April; Planktos expects to see blooms this summer.

Sun-Refracting Space Shields

THE GOAL: Lower the global temperature by launching 16 trillion refractive shields into orbit to literally shade the planet.

THE PLAN: The brainchild of Roger Angel, a professor of astronomy and optical sciences at the University of Arizona, the 3-ft.-wide shields would refract about 2 percent of the sun's rays. Angel proposes launching the shades, which have a 50-year life span, in batches of up to 800,000. The cloud of shields would be more than 62,000 miles long.

TIMETABLE: Angel estimates the project could take 25 years -- and trillions of dollars -- to launch.

Artificial Trees

THE GOAL: Trap CO2 using thousands of giant artificial trees, which would be equipped with sodium hydroxide-based filters.

THE PLAN: To mitigate humanity's total CO2 output, Columbia University professor Klaus Lackner estimates we'd need up to 500,000 fake trees. The structures would be the size of industrial windmills -- and might look more like giant spatulas. One obstacle is finding a way to get the CO2 out of the filters so they can be reused.

TIMETABLE: Before he can plant 500,000 trees, Lackner needs to build at least one prototype.

Atmospheric Sulfate Infusion

THE PLAN: Using eruptions from Mount Pinatubo as a model, Thomas Wigley of the National Center for Atmospheric Research suggests infusing the atmos­phere with 5.5 million tons of sulfur dioxide every one, two or four years. Combined with a CO2 emissions cap, Wigley estimates the infusion could halt global warming for up to 50 years.

TIMETABLE: Anyone's guess, since scientists have yet to settle on an infusion method.